In order to prevent cross-talk due to an RC delay, an air gap may be formed between wiring structures each having a copper wiring and a barrier layer covering a bottom and a sidewall of the copper wiring. In order to form the air gap, a portion of an insulating interlayer between the wiring structures may be removed, and an upper edge portion of the wiring structure may be also removed. Thus, an electric field may concentrate on an upper edge portion of the copper wiring, which may deteriorate the reliability of the semiconductor device including the wiring structure.